text:
Why don't airliners use noise cancelling?
Some cars have started using noise cancelling in their cabins, through the speaker system. It's a well established technique for dealing with low frequency noise like engine rumble and wind noise.
So why don't modern airliners use it?

Welcome! Noise cancelation works by injecting a signal with opposite phase that cancels the original signal. As phase is varying with the distance from the source, this works only in a small area, but in large areas like a cabin, the phase is not constant within the whole volume, so the cancelling phase must be different according to the location in the cabin. This would require using headsets for instance. note that injecting out of phase noise, adds noise heard according to an interference distribution. A lot of noise!

@mins I see your point, but noise canceling has both a theoretical and 1 practical side. Physics can cover the theory, but it can't address the practical issues that are unique to aircraft/cars/buildings etc. That's an engineering question and I think any aviation-specific aspects of noise canceling are certainly on-topic here.

@Pondlife: Good point, I've retracted my vote.

The Bombardier system works because prop noise has a well defined frequency spectrum (as shown in the link) at known frequencies - it's easy to measure the prop RPM accurately - and the source of the noise is localized (the prop wake acting  the airframe). Neither of those conditions apply to the OP's "engine rumble and wind noise."

Man, if they could cancel the people next to me I would pay double.

@TylerDurden Pay double, and you won't have at least one of the people next to you...

@MichaelKjörling the joy of overbooking mean that you might :D

First, some airliners do use it - the Bombardier Q400 uses a NVS (Noise and Vibration Suppression) system to reduce cabin noise. Basically, it uses devices called Active Tuned Vibration Absorbers (ATVAs) mounted on the fuselage frames to 'cancel' the vibrations from propellers and outside noise, thereby quieting the cabin.
However, there are some issues with using active noise cancellation in aircraft:

The aircraft cabin is quite big and complex, and it would be very difficult to achieve noise cancellation over the entire volume; as active noise cancellation depends on the cancellation of sound waves using opposite phase, it works best in small, confined spaces. If the waves turn out to be in phase in a region, the sound would be doubled - not a good result.
A significant contributor to the noise inside the cabin is the wind outside; this is usually random and the frequency spectrum is also quite wide, resulting in difficulties in noise cancellation.
Noise cancellation is effective mostly when the frequency of the source is constant, which is not usually the case (the props are an exception - they lend themselves well to noise suppression)

Instead of active noise cancellation, aircraft manufacturers are putting more energy in reducing the noise itself:

Better engines, which has lesser noise through the use of chevrons, etc.
Better modelling of aircraft, so that the fuselage design minimizes the noise due to wind.
Better damping and cabin design, so the noise produced (for example, due to air conditioning and ventilation) is reduced.

“It's a well established technique for dealing with low frequency noise”

– exactly. Noise cancellation works precisely if, and only if, the area you try to shield from the noise is significantly smaller than the wavelength of the sound you try to cancel, because then you can ensure that the anti-sound signal will in fact interfere everywhere destructively with the environment noise. Wavelength scales as $\lambda = \tfrac{c_{\mathrm{s}}}{\nu}$, so it gets ever smaller as the frequency $\nu$ increases.($c_{\mathrm{s}} \approx 343\:\mathrm{\tfrac{m}s}$ is the speed of sound.)
As soon as the size of the room you try to apply this to is larger than the wavelength, it is inevitable† that the artificial signal will in fact interfere constructively on half the space, i.e. it will in many spots actually make the problem worse than it was by itself!
In a car, you can go quite far – the space is really small, and LF rumble has a generous wavelength – up to ~100 Hz you can be sure that it at least won't interfere constructively anywhere in the cabin.
Quite different in case of an airliner – not only is the cabin much bigger, also, jet noise has much more high-pitched components. Hence it is completely hopeless trying to cancel this sound with open speakers. It is possible to cancel it directly at the ear, with noise-cancelling headphones. But these are already available individually, so it's not something the airline needs to worry about!

†Unless you can exactly predict the direction of the interference noise. That is only possible if you know a priori the exact phase of the source noise. As said in the other answer, this is actually possible to some degree with turboprops (which also have more low-frequency components), but not for jets.

I think the proportionality constant between wavelength and frequency is usually only called c when it's the speed of light.

@PeterCordes: it is often used for sound speed too, but I agree that this probably isn't a very clear symbol choice.

@SteveV. Note for future authors: "iff" is correct but it's not an abbreviation that I'd expect people outside mathematics and maybe engineering of physics to understand. In the interests of comprehension, I've expanded it to "if, and only if,".

@DavidRicherby It's a very useful word. Iff we use it more often, more people will understand it. Especially on a site like aviation.

The main problem in a large cabin is, "What do you cancel?"
The noise in an aircraft is different depending upon where you sit. The engine noise is different whether you are in front of the engine or behind it.
Canceling the noise in one place in the cabin would increase the noise in another.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Can a person with unilateral anosmia in the right nostril become a commercial pilot with a class I medical?
I had a minor road traffic accident in November 2014, since then I cannot smell through my right nostril, where my left nostril is working normal. I am looking to know if you know any pilot you have met with who has no sense of smell or lost it due to any event like accident in my case and is still flying.
I am interested in FAA and DGCA India regulations.

Welcome to aviation.SE! Which country's medical standards are you asking about?

There are commercial pilots who are blind in one eye, missing an arm, and have history of heart disease. Getting a waiver for this should be no problem.

@StephenS  The FAA medical form pretty well requires disclosure of all known issues; to intentionally withhold relevant information would be a criminal offense.

It's about commercial pilot career irrespective of country specific standard like FAA, USA or DGCA India. However, as I will be applying for FAA and DGCA, so you can take these two as specific for you to answer. Thank you

@StephenS There are broad "ever admitted to the hospital" and "any surgery" questions that would probably catch the genesis of what's being discussed here. The additional test they've ordered (see OP's comments on my answer below) sound like they're interested in other ramifications of the trauma that led to the loss of smell. Having reduced sense of smell by itself may be less their concern than what else may be out there & not fully realized.

@RalphJ Fair enough; earlier comments deleted.

I can’t find any mention of a sense of smell criteria in the FAR/AIM. There are requirements for hearing, speech, and balance (vertigo) having to deal with the nose. That being said, a sense of smell may alert you to a problem in the aircraft or a fuel contamination. Since there is no Reg for it, the FAA is probably more concerned with the root cause due to the accident rather than the effect itself. Since this sounds like a rare condition, it’s doubtful there are many, if any, other pilots with it. And, even fewer walking around discussing it with their colleagues.

That being said, I do know of one pilot who lost her medical due to vertigo. She was able to overcome the vertigo, regain her medical, and return to work as an air traffic controller. She worked and flew for years after that until the vertigo returned. Although, she could no longer fly, she continued working as an ATC until vertigo finally forced her to retire years later. This was not caused by an accident, though. So, my guess that the FAA would probably be concerned with the neurological effects of the accident regardless of how they presented themselves is still probable.

We aren't medical professionals here, and no Aviation Medical Examiner (AME) posts on this board as far as we know.
The best answer is to schedule an appointment with an AME and have him review your case. If the answer is "yes" you can get the medical, this is a cost you'll be paying anyway (and I'd suspect that is the answer you're likely to get). If the answer is "no," better to get it from an authority, rather than an internet message board.
AOPA can help you locate an AME who specializes in "interesting" cases, some of whom may well be able to review everything over a phone call or video chat, at least to the point of recommending your best course of action.
Go with an AME's answer, rather than ours. Best of luck to you!

Thank you for answering, I have already submitted FAA Form 8500-8 way back, currently  it is differed to FAA for issuance where they have asked for more neuropsychological testings which I will be taking. I wanted to know if there are pilots with anosmia you know about any already flying out there with airlines.

That will be the definitive answer, then. Hopefully the other test can confirm "no other issues" and you'll be good to go. Sadly, nothing any of us can post here has much chance of overriding their need to see more tests. That said, I've seen plenty of guys who went thru some bad stuff & had to take a lot of tests (to rule out rare but serious 'other conditions' that might show up later), but got their medicals back when it was all done. The FAA is cautious & thorough like that, but not draconian. "Yes" is still an entirely possible answer for you. Best wishes!

It would be very bizarre to deny a Cat 1 because of lack of smell on one side when there are Type 1 diabetics flying airliners in Canada and UK.

@nick012000 I expect AME is Aviation Medical Examiner :)

@JohnK A sense of smell may be needed to avoid disasters. Things like a smell of burning or fuel can be VERY bad signs. Also, does this loss of smell also means reduced "airflow" through the nostril? At high altitude, will that reduce the oxygen levels to dangerous levels where brain function may be impaired? I think this is the sort of questions they may ask and the tests they may do. This is my guess, and in no way,s ahpe or form based in deep knowledge of aviation.

@IsmaelMiguel 1) he doesn't have full anosmia, only in one nostril; 2) in commercial aviation there are generally 2 pilots on every flight; 3) I'm not sure how likely it would be for a commercial pilot to smell a fuel leak, given that fuel is generally stored in the wings and any fuel scents would most likely be noticed by passengers/cabin crew before the pilots can; 4) A fire outside the cockpit would be similar to point 3; 5) modern plans have tons of sensors for detecting fires and fuel leaks anyway.

@Nzall Those are good points, yeah. I forgot that there are systems in place to try to suppress fires. And yes, I know it is in just one nostril.

FAA Regulations for First Class airmen describe the medical requirements for ear-nose-throat related conditions in §67.105   Ear, nose, throat, and equilibrium.

Ear, nose, throat, and equilibrium standards for a first-class airman medical certificate are:
...
(b) No disease or condition of the middle or internal ear, nose, oral
cavity, pharynx, or larynx that—

(1) Interferes with, or is aggravated by, flying or may reasonably be
expected to do so; or
(2) Interferes with, or may reasonably be expected to interfere with,
clear and effective speech communication.

(c) No disease or condition manifested by, or that may reasonably be
expected to be manifested by, vertigo or a disturbance of equilibrium.

There are explicit requirements for visual acuity, but not for olfactory ability.  Still best to consult with a professional examiner to be sure, but I've not heard of pilots being tested for sense of smell.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

sort: votes


text:
Would a wingtip stall still be bad if there was no aileron there?
If there was no aileron on the wing tip, would a tip stall still be bad compared to a root stall?

Short answer: yes.
Control effectiveness: We do care about ailerons
The fact that there is an aileron at the wingtip implies that flow separation (stall) at the wingtip results in significant decrease or complete loss of aileron effectiveness during a tip stall.  As a result, as you imply by your question, designing aircraft to begin their stall at the wing root (or, otherwise, to implement some device such that control effectiveness is maintained at high angles of attack) is a typical practice.  Peter Kämpf has a very detailed answer about this (and other topics related to stalls in swept-wing aircraft) here, and there's another answer from AEhere Supports Monica and another one JohnK that gives a summary as well.
But what if the aileron wasn't there?
However, if the aileron did not exist, loss of lift (and increase in drag) at the wingtips is still of great concern.  Insofar as the stall itself goes, when I think of the dangers of losing lift at my wingtips, I think of spins, which look like the below.  This "classic" spin entry is caused by a sideslip (in this case, to the left wing) with the stick pulling back to put the aircraft into a stall.  In this case, the left wing is operating at a higher angle of attack than the right and stalls first, creating the conditions for a spin.

When I did spin training in a Grob 103 sailplane (with your typical control setup of elevators, rudder, and ailerons), the mantra was put the stick neutral, push the rudder opposite the spin, then recover in pitch.  The ailerons were not a part of the recovery (until, perhaps the very very end once the airplane has started flying again and you find yourself not quite level).  This is not the case for all stalls: forward stalls (stalls with near-zero sideslip and coordinated controls) are relatively simple to recover from, and I've held Grob 103s in a forward stall for extended periods of time (though they also have pretty benign stall characteristics).
Turning stalls or stalls in uncoordinated flight are where you get get in trouble with spins, and the more your airplane wants to stall at the wingtip first, the more dramatic (and interesting) will be the aircraft's departure from controlled flight.  This is, in part, because of the yawing and rolling moment caused by the lift and drag differentials between wings -- and, if those differentials are between wingtips, the moment arm for those forces is that much more.  Note: you are not usually using ailerons during this maneuver--in fact, if ailerons are deflected counter to the direction of the spin (per intuition), it can make the spin worse.  That said, Peter Kämpf pointed out that using the ailerons to point the aircraft in the direction of the spin can make it easier to recover from.
However, more to the point: regardless of if ailerons are present or not, rolling an airplane usually produces a restoring roll moment.  As I move a wing upward, per the diagram below, the wing "sees" air coming from above the wing, which decreases the angle of attack (relative wind coming from above the chord line is a negative angle of attack).  The converse occurs for a wing that is descending.  A negative angle of attack corresponds to a decreasing lift coefficient and vice versa: hence, the lift of the wing with change with the wing's motion and, in some way, "damp" the wing's heaving motion.

However, keep in mind that we are talking about something a little more nuanced.
If we go back to the picture of an airplane entering a spin (above--1st picture), the right wing is close to stall and is operating at a very high angle of attack and a relatively large lift coefficient.  The left wing is stalled (operating at an even higher angle of attack than the right wing): it's lift coefficient is much lower than that of the right wing: the airplane wants to roll.  However, if we reference the chart of angle of attack vs. lift coefficient below (stall is denoted by the first peak of lift coefficient around 10 or 12 degrees angle of attack), the stalled wing is operating "post-stall" or, potentially, somewhere in the 15-20 degree range where an increase in angle of of attack no longer corresponds to an increase in lift coefficient--but, rather, a decrease.  Even if the stalled wing if past this range, the lift coefficient increases relatively slowly, and drag increases much faster, slowing the wing down and rapidly decreasing the wing's lift production (lift is directly proportional to the lift coefficient, but changes with the square of velocity).

In short, the aircraft already wants to roll towards the stalled wing and the lift coefficient of the stalled wing is, potentially, decreasing as the wing drops (which increases the local angle of attack).  Now, the opposite wing is moving upward and, as such, its angle of attack is decreasing and it's lift coefficient (which is already higher than the stalled wing) is also decreasing.  However, drag is also decreasing as well, so the wing can travel a little faster - and, thus, produce even more lift.  If the lift production of the stalled wing remains less than that of the other wing, the aircraft will continue to roll.  Which, as you might imagine, is a $Bad \hspace{1ex}Day^{TM}$ (unless you can get both wings flying again).
Peter does mention some issues with tip stalls in the answer I linked earlier as well, specifically in swept-wing aircraft.  In swept-wing designs, lack of aerodynamic or geometric washout resulted in substantial nose-up moments at stall (when the wingtips stalled first) due to the physical geometry of the aircraft.  The tip of the wing, which was no longer producing significant amounts of lift, is probably located behind the aircraft's center of gravity.  As a result, loss of lift at that location would decrease the nose-down moment generated by the wings, which is exactly the opposite of what you want to be produced when in a stall.  A stall at the root would obviate this.  In short, how bad the results of a wingtip stall will be are tied to the design of the aircraft -- and swept wings, in most cases, are a design choice tied to lateral stability or design for high speed flight.  A design choice for one characteristic influences others.
But what if we didn't use ailerons at all?
The most complete answer would speak to how tailerons or elevons (or a horizontal tail whose surfaces can be actuated independently of each other) change spin recovery technique.  For example, I was reading this document on F/A-18C/D spin recovery technique, and it notes that proper spin recovery in the F/A-18 is accomplished by a lateral stick movement.  The Hornet, apparently (can't say I've flown one, but I know there are folks on here who have), has a very violent stall/spin departure mode in which the stick should be kept neutral, but, once the spin is established, the stick is moved laterally to recover.  Examples I've seen go into the direction of the spin, which would match with the prior note about turning into the spin with ailerons.  I anticipate that this leverages the sheer size of those horizontal surfaces and that they have some degree of effectiveness (as opposed to the rudders, whose effectiveness may be reduced due to the wake from the other vertical tail).
Regardless, with reference to the question of "would a tip stall be bad if I was using tailerons anyway", the earlier points about how the severity of the stall is tied to aircraft design still stand.  How bad it is depends on the design of the aircraft, how the CG is located relative to the wing, how pitching moments are produced and balanced in the aircraft's design, and so on -- all factors that are not necessarily tied to the selection of roll control surface.

Ailerons in direction of spin help to make the spin deeper, so recovery becomes easier. With or without ailerons, a tip stall might induce an autorotation around the roll axis (roll damping becomes positive), something that can ruin your day when it happens at low level.

Ah!  Excellent -- thank you!  I'll edit with this.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
Is it possible to give an endorsement via text message or email?
Is it possible to give an endorsement to student pilot via email or text message?
For example, I gave an endorsement to my student for a XC. However, he stuck at the destination airport after the weather gets bad. On the next day, the weather became good enough to come back. But, he needs another XC endorsement to fly solo.

How can he receive an endorsement to come back?
Is it possible to send an endorsement via text message or email?
Is it okay to receive an endorsement from somebody CFI at the destination airport? (Let's say they don't know each other.)

That would be great if someone could help me!

this may be a dumb question, but isn’t the original endorsement good for the return leg as well?  Or do they expire after 24 hours?

For questions about regulations and what's legally possible, please always tell us which country or regulations you're asking about. I've added the faa-regulations tag to your question because it looks like that's what you're asking about. If I'm wrong, please edit your question to add the correct information.

This question might answer what you're asking. At least questions 1 and 2; for question 3 see here.

Easy, peasy. Fill out a label/sticker with the endorsement printed on it. Then, all you have to do is sign it and place your CFI number on it. You can then either scan it or take a photo of it. Your student can upload the scanned document or photo into an electronic logbook. If they do not have an electronic logbook, they can print out the endorsement at the FBO to put into their paper logbook. When you and the student are together again, you can place the actual label/sticker in their logbook. Alternatively, you can use regular paper. Then you can cut the endorsement into a manageable size and tape it into the logbook. Also, if you and your student use the same software for your electronic logbooks, many have a function to sign endorsements electronically even at a distance (through the internet).

Thank you again Dean F. That is great explanation!!


text:
How can a large passenger aircraft's owner remain unknown?
I'm reading through TheStar's "Malaysia Airports seeks owner of three Boeing 747s abandoned at KLIA" article and I can't stop wondering, why I don't understand it or how should I understand it?
How it is possible in 21th century, that knowing large passenger aircraft's (a) type, (b) current location and (c) registration it is still impossible to find actual aircraft's owner in a matter of minutes?
Don't we have aircraft's databases, to obtain this information? Or to use it to track any passenger aircraft latest flights? Is it possible, that Kuala Lumpur International Airport does not have any records or tracks of what (owned by whom) and when landed on their grounds?
I know that this isn't possible, but for a newbie like me this article sound like a joke rather than a current reality in aviation industry today.

Wish I had the kind of money it takes to casually misplace a billion dollars worth of planes...

With corporate transactions, and possibly a bankruptcy or two, not knowing (or disagreeing on) who owns what exactly can happen very quickly.

I could agree to your point of view, but there's one thing. IMHO during bankruptcy, a plane as valuable as even 20 years old B747 (not mentioning three of them) would be an important asset. Important enough to not just leave it somewhere. Company that goes down has a lot of debts. Many of these could be paid by using that asset. Am I right? I know, that these are just speculations, but in my opinion they support theory, that this article says about something strange or even hard to believe.

If the operators of the bankrupt company are dishonest then they may lie to the bankruptcy court about it's assets either with the intent of stealing them later or just because they want to screw the creditors.

@trejder But you have to pay the parking fee first. KLIA charges 0.5RM for every 10sqm2 outdoor parking every 12hrs. Parking cost 260 thousand USD for each year.

It could be that the current owner doesn't want to be found, whether because he/it owes money that he doesn't want to pay, is attempting to avoid taxes, or any number of other nefarious reasons. Pure speculation, of course, but more likely than Delta (or Air Atlanta Icelandic) pilot getting drunk at the airport bar, walking to the hotel and forgetting where he parked... :)

@corsiKa While that would be nice, in this case, the planes are not worth anything close to a billion. A few million, perhaps. They're over 35 years old and probably not airworthy after sitting there that long. The cost of paying the owed parking fees and restoring them to airworthiness to move them may well exceed their value.

There is a very good chance the planes will never be claimed.  The debt on the plane is more than its worth.

It's likely these planes aren't airworthy.  Furthermore, it's not that they can't trace the owner, it's that they are publishing the required legal notices in case someone else has an interest in them.

Every country handles aircraft registration differently (but generally similar). Im sure Boeing could tell you who they originally delivered the airframe to but if it was sold from there it could legally go anywhere and would only be subject to local registration legislation.
Here in the US you can look up aircraft owners by N number but not all countries may keep a record like that and as far as I know there is no global aircraft registry.

it is still impossible to find actual aircraft's owner in a matter of minutes

Knowing who the owner is and finding the owner are two very different things.
According to this article

Several aviation databases list the Boeings -- identified by their
  call signs TF-ARN, TF-ARH, TF-ARM -- as belonging to leasing firm Air
  Atlanta Icelandic, but that company says it sold them in 2008.
Since then, the aircraft appear to have changed hands several times.
Malaysia Airports says it's entitled to sell the Boeings under the
  country's civil aviation regulations if no owner comes forward.

So it seems they do know who owned them at some point (most likely the last people to put readable registration numbers on them).

Thanks for a good answer. I still can imagine, though, that KLIA doesn't have any record on when these planes landed for the last time and what was plane's operator during that last flight.

They may know who landed them and when but if the planes were parked and sold (multiple times at that) the responsibility lies with the current owner and the original seller may be of little help aside from a courteous finger point to the next link in the chain.

Do you mean, that they were parked like months or years ago and sold during parking? Who then paid for parking fees? Why did KLIA started the case right now and didn't put any interest during those months or years, these planes were parked on their grounds. This certainly is a mystery case for newbie like me.

Thats possible the facts all still seem a bit unknown, maybe someone was paying, maybe KLIA over looked the fact that no one was paying or maybe KLIA was billing someone and only now has sent it to a collection situation.  While I admin its a strange situation sometimes the natural course of these events takes time to unfold. Someone may step up tomorrow as the owner, who knows.

@trejder Well, apparently, nobody was paying for the parking fees, which is why the airport is trying to sell the planes to recover the fees it's owed.

@DavidRicherby Sure thing. But the question is not about, why airport is trying to sell these planes (quite obvious, as you point out), but how it is possible in 21th century, that airport is unable to establish, who is that planes' owner. Notice, that this article is not talking about the fact, that airport can't get owner to pay his dues. It is about the fact, that airport does not know the owner. This is the strange part of the article (and the reason for this question) for me. Not the part about selling these planes.

@trejder You brought up the parking fees and asked who is paying them, so it's a bit rich of you to ding me for drifting off-topic when I'm responding directly to you. Clearly, if they knew who paid the parking fees, that would give them information about who owned the planes. The fact that they don't know who owns the planes strongly implies that the parking fees aren't being paid.

If at one moment AAI owned the aircraft, then unless they show an evidence of the sale, they are assumed to be the owner and must pay. If they are not the owner then the sale evidence will include the identification of the buyer. The story being still unsolved means important details are missing.

@mins According to CNN, it appears that the aircraft have been sold several times since AAI owned them, so it appears that they already have produced evidence of having sold them.

@reirab: So the same process should be possible until a buyer cannot show any evidence of a sale. This one is the assumed to be the owner and a legal action can be initiated if necessary.

There's certainly some missing details in that story. Two minutes with Google shows that (a) the prefix "TF" refers to Iceland, and (b) those three aircraft were most recently registered to Air Atlanta Icelandic, some sort of charter/cargo operator.
What's missing from that news story is that surely the Malaysian authorities have already done the above, and have been unable to contact the registered owner for whatever reason.
Interesting is that the Air Atlanta Icelandic fleet as listed by ch-aviation does not include those three registration numbers. So maybe they've been sold to someone else.

http://www.thestar.com.my/news/nation/2015/12/08/air-atlanta-returned-aircraft/

The article in the Guardian said that they think they know who the owner is on paper, but that company isn't contactable.  Taking out advertisements in major newspapers (within the same jurisdiction, then covered as news by the world's press) is likely to be a step towards giving due notice before reposessions proceedings can start, to give the real owner time to respond.

+1 for first legal steps toward being able to lien against them or some sort of similar asset takeover.  I wouldn't be surprised if these aircraft were left in this particular location because of the specific rules in the jurisdiction.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Was a 7300-mile non-stop flight possible in 1979?
I'm listening to the On Wings of Eagles audiobook by Ken Follett and found some information about a non-stop transatlantic flight between Teheran (IKA) and Dallas (DFW). GCM says that this is 7,300 miles and Google says that's 11,750 km.
Was there any aircraft capable of performing such a flight in 1979? If yes, then which one?
It was expected to travel with about 10-15 people on board and non-stop flight seems to be essential (at least to the author, because I completely don't understand the reasons why such a flight couldn't take a re-fueling break at some European airport once clear of the dangerous zone of Iran's / Middle East's airspace).
The author's choice of either a Boeing 707 or 727 seems to be completely incorrect, as according to Wikipedia there wasn't any version of either of those aircraft capable of flying 7,300 miles non-stop (or I'm missing something). The longest range mentioned is 10,650 km in the case of the B707-320B.

The 747 could do it.

"Longest mentioned range is 10,650 km" under certain conditions (cargo weight, passengers, altitude, speed, wind, etc), but how long in the conditions of the book? Was the aircraft modified with an additional tank?

@mins Not directly explained in the book, but given conditions of plot action (chartered plane able to be ready as fast as possible) I assume that we're talking about completely unmodified plane with no additional tanks etc.

"1978 - Omni leases a Boeing 707 to Ross Perot for rescue of EDS employees from Tehran. The story would later be chronicled in Ken Follett's bestselling book 'On Wings of Eagles'" (source).

Usually, the "Maximum Range" quoted on Wikipedia is at the Maximum Take-Off Weight, something that probably wouldn't happen with 10-15 people on board. To get the true range you would need to have the aircraft performance charts.

BTW, you don't need to go via GCM and Google to get distances in kilometers: you can select your units in GCM.  (Here's IKA-DFW in km.)

Even for zero payload, no B707 model is able to fly more than 6000nmi (11111km). B727 even has less range.
However, Iranair planned to run Tehran-LAX flight, which length is 12222km, but never materialized because of 1979 revolution. The flight could have been operated by the 747SP (introduced in 1976), similar to their Tehran-JFK route.

As in my comment to Dave's answer, it seems, that you confirm my assumption -- it is possible in general, but author's selection of 707 is a completely wrong path. Am I correct?

@trejder Maximum range may vary for other reasons like jet stream which does not take into consideration on the table above.

Your image links are broken.

Sure it was possible as for the list of planes that depends on if you consider the planes in their base configuration or not. Just about any plane out there could be fitted with Ferry Tanks allowing for ranges that are well outside its quoted maximum range. As you mention the aircraft only needs to hold 10-15 people, in the spirit of completeness for what its worth a plane like a 747 can fly a lot farther if there is only 15 people on board and the rest of the plane is effectively a flying fuel tank. While this may not be the immediate case there the idea is similar.

Please, consider my comment added an hour before your answer. It seems -- due to story plot (an extreme rush) -- though not clearly stated in a book, that we're talking about unmodified plane only (no external tanks). Plus: it seems, that even though 747 can do this, author's selection of unmodified 707 (727 also considered, but rejected) is a wrong shot. Can you confirm that? Thank you.

Sure. A B-36 produced from 1946 and onwards has a range of approx. 10.000 miles according to Wikiepdia: https://en.wikipedia.org/wiki/Convair_B-36_Peacemaker#Specifications_.28B-36J-III.29
According to the book "B-36 - Cold War Shield" a regular long-range crew numbered around 15 people, plus possible obeservers.

Don't think any were still flying by 1979, though!


text:
After the Covid pandemic, will there be an aircraft manufacturer which produced a combi aircraft anymore?
On this covid pandemic, there will be many changes in all of air travel, one of them is Combi aircraft to be rebuilt again.

Welcome to the stack! We’re glad to have you, and look forward to hearing more from you in the future. Please keep in mind that this is not a discussion forum, and opinion-based questions should be avoided. Questions like this can’t have a satisfactory, objective answer, since no one can predict the future or how the covid-19 outbreak will progress. I hope this doesn’t discourage you from posting again. Have a nice week.

The business case for combi's has little to do with air travel in that regard.  The only significant change you will see industry wide, as air travel recovers over the next several years, is every airliner adding HEPA filtration to its cabin air recirculation system.  It's a good time to be a manufacturer of HEPA retrofit filtration kits.

So actually, Combi is unrelevant now? Why?


text:
How much aluminum was used in the Boeing 727?
What is the weight of aluminum used in the Boeing 727 fuselage? Do you know where I can find it? Any manual or site or something like that?

It may not be possible to provide a precise number for a question with so many variables. Likely, the amount differed between variants. Without speaking to a materials acquisitions director from Boeing in the 70s and 80s, the precise number is probably not available.
That said, this airplane scrapyard website mentions that aluminum accounts for approximately 20% of the weight in a Boeing 747. Going by that same rubric, one might estimate that a 727 would contain approximately 41,900 pounds of aluminum.


text:
What is the reason for different number of front nozzles on commercial aircraft?
As we observe in commercial aircraft, that there are four or two front end nozzles for gas emission in the air.
What is the reason for this variable of 4 or 2 nozzles?
Why is it not a constant?

Got a photo of what you are talking about?

I’m unclear of what you are asking.  Are you talking about engine intakes?

@PrashantAkerkar I suggest you have a look at this question: How do jet engines work?

the "front-end nozzles" you mention are the air inlets for the plane's jet engines- one inlet per engine. The outlet that emits exhaust gases at great speed is in the rear of the engine. Some jets have only one engine, and one inlet. Some have two, some three, some four engines; the B-52 has eight engines and eight inlets.
Greater numbers of engines are used to power bigger, heavier planes. Early engines were not very powerful and so older planes that were big and heavy (B-47, B-52, 707, DC-8, 747, etc.) had many engines. Modern engines are much more powerful and so fewer of them are needed, even on big planes.


text:
Front and / or Rear Tires Doors or Windows testing in Aircraft
I would like to know before the landing takes place, is there a way out for the pilot to know whether the doors or windows for the Front and Rear tires of the Aircraft will work 100%?
If i am not wrong, the doors or windows are opened while landing for the Front and Rear tires to open.
In case the door or window which i am referring does not open, will it not be a risk for landing?
Is there a technical term for the door or window part of the aircraft which i am referring?

I think the term you are looking for is landing gear door.

"is there a way out for the pilot to know whether the doors or windows for the Front and Rear tires of the Aircraft will work 100%" Very few things in life are 100% guaranteed. There are a number of indications that can tell them it may not be working, but that's not to say something may happen later that isn't caught by those methods.

Sorry, but I am downvoting because it is not clear whether you are asking about landing gear door operation, testing landing gear doors, sequencing gear assemblies from up and locked to down and locked, or somehow automating the application of brakes during different phases of flight.  (per your comments)  We can help you edit the terms if we understood better what you are actually asking.  And what are the pictures intended to illustrate?

I am trying to automate the tires opening and closing for different plane motions. Plane at rest on ground, Plane in motion on ground preparing for take off, Plane in Sky after take off, Plane again on ground after landing.
I feel the Transaction from Plane in Sky to Land is difficult to automate. i e Tires closed to Tires opening for landing.
Plane at rest on ground, Plane in motion on ground will require the Tires to open and work while the Plane in Sky the tires do not be required to be open so they are in closed position. Tires open - UnLocked action, Tires closed - Locked action.

Thanks. I am also researching on whether Automating the function of the landing gear classify as a Machine learning or Artificial Intelligence technologies business use case in Aviation industry.

@Digital Dracula, glad I'm not the only one...  I voted to close for lack of clarity.

Oh yeah, and for those who didn't bother following our other discussion over to chat, it turns out that "rubber sensors" means tire pressure monitoring system, and that this function is also a part of the question, and under consideration for possible automation.  Whatever that might entail...

There are no 100% guarantees in life, certainly not in aviation. But in the interest of safety pilots have multiple indications available, and options in case things go wrong.
In most planes the landing gear and gear doors are either hydraulically or electrically operated. The hydraulic and electric systems are critical throughout the aircraft, so there are indications to the crew that can show if there are any issues with these systems. There is also usually an alternate method of extension in case the primary system has issues. Gravity typically helps.
Once the gear is extended, it gets locked in place. The crew will have an indication of whether each landing gear location is down and locked, typically with an indicator that shows red while the gear is in motion and turns green once it's locked. You can see the indicators in the image below for Nose, Left, and Right gear.

If there is an indication of an issue, pilots may sometimes fly a low approach to the runway without landing to let ATC look at the gear to see if everything looks normal. It's possible that the gear is down but not locked, or locked but just not indicating properly.
If there are issues, the crew must simply work their checklists to try as best they can to get the gear down, and then land carefully. Airplanes are designed to land with some or all gear up in case these issues happen. Rescue crews can be on standby to help passengers and crew evacuate in these situations.
In 2011, a 767 had to land with its gear up after the crew was unable to get the gear to extend. The airplane was a total loss but no one on board was killed or injured.

Thanks for the information provided. I would like to know whether the Nose (Front) & Main (Rear) Landing Gear are automatically locked or unlocked instead of Human manual intervention?. If not, do you feel this can be automated taking into consideration as Locked while plane in air (Tires not touching the ground) & Unlocked (Tires touching the ground) using sensors.https://www.google.com/search?client=ms-android-lava&sxsrf=ALeKk022XyFnLlMV32OAAEPYnkxLeGuwuA:1628734034281&q=rubber+sensor&spell=1&sa=X&ved=2ahUKEwjfpa-Ms6ryAhVbQH0KHYPcBQMQBSgAegQIARAC&biw=360&bih=592

What do you mean by "automated" vs "manual intervention"? There are a series of mechanical linkages and hydraulic actuators that control extension and retraction of the landing gear that begin a designed sequence when the handle is placed up or down.  Are you suggesting a system for removing the need to move a handle?

The "lock" in this case is not like a padlock with a key, and the pilots have to manually set the padlock. "Locked" means the mechanical actuators are fully in place and the safety mechanisms that prevent the gear from being pushed back up when the plane lands have properly engaged.

Thanks Michael. The Handle is there in case Human manual intervention is required for locking and unlocking the Gears.By default the Nose & Main Gear are automatically Locked or UnLocked using sensor technology. Example : Three stages of motion. 1 Before taking Acent in sky, plane on ground so Gears are Unlocked. 2 After Ascent in sky, plane not in ground so Gears are Locked. 3 Plane landing on ground so Gears are UnLocked. All the Above motions can be automated for the gears by default using rubber sensors or any other means? Note: The Handle is there in case manual intervention is required.

The handle is there to manually initiate the extension or retraction sequence.  The gear is locked into place either up or down with mechanical latches.  There is no separate manual locking operation required under normal operation.  Light indications in the cockpit are activated by simple electrical position switches.  Otherwise I'm not clear on what you are either asking, or mis-explaining...

Thanks Michael. I got your point. I was just curious to know whether the gears actions i.e. locked or unlocked positions can be automated depending on the motion whether the tires do not touch the ground (Locked - Plane On Ascent- In Sky) or touch the ground (Unlocked - Plane Before Ascent, Plane After Landing on Ground). The Handle will be always there for manual intervention for Gear locking and unlocking mechanisms. Thanks for your assistance.

Almost anything can be automated, but in this case, why?  Simple mechanical linkages work just fine, automation would just introduce an additional failure mode.
Also, your description of locked or unlocked during different phases of flight doesn't really make sense... i.e. "Unlocked... plane after landing on ground" What does this even mean?  The gear would collapse if it wasn't locked down on the ground.

Thanks Michael. I got your point. It will be difficult to build the automated logic when the plane is going to land in ground. Because the Gear has to be brought from locked to unlocked position before touching the ground. How automatically this action can be performed that i will be landing so unlock, so in this case manual intervention will be required by the pilot for unlocking? Maybe the first two motions can be automated i.e. Plane before ascent, tires touching the ground, so unlocked and Plane in Ascent, tires not touching the ground, so locked using rubber sensors technology.

Thanks to everyone who participated for answering to my queries about Aircraft Tires.

When you say locked, are you talking about the tires rotating?  Because that is different...  (I assumed you were referring to the struts and braces themselves)
And I don't know what you mean by "rubber sensors", but the antiskid system can sense wheel rotation and is normally programmed to send a brake release signal with weight off wheels to prevent landing with the brakes applied.  I guess in that sense it is automated...
Anyway, I think we may be having some language barriers that prevent clear communication.  (since the title question is more about the gear doors...)

Thanks Michael. I understood all your answers to my queries. There is no language communication barrier. I thank you and all who helped me with my queries on Aircraft tires.

Let us continue this discussion in chat.


text:
How do airlines replace a pilot at the last minute if they're unable to fly?
I would like to know what decision do the commercial airline carriers take when there is emergency case of a pilot who cannot fly the plane because of personal emergency conditions?
Emergency conditions could be the pilot falling sick with a medical emergency, family member, close relative death etc.
The event has happened just a few hours before the final plane departure.
Does the co-pilot fly the plane in that case? Do the specific airline carriers always have pilots in reserve?

Not really an answer, hence written in a comment. I remember about a year or so ago there was an incident all over the news in the UK (I believe it was RyanAir) where the first officer didn't show up for the flight in the morning and couldn't be reached. As it turned out, one of the passengers was an off-duty pilot from the same airline - and upon learning of the reasons for flight delay, offered to serve as the second pilot for the flight.  He did end up being the first officer for that flight.  This was a UK to Spain flight.

The airplanes can't depart without the minimum crew, which means 2 pilots, or 3 if there is a Flight Engineer.
The airlines have "Reserve" and "Ready Reserve" types of duty to cater to this, and pilots will be scheduled for one or the other at different times (depending on seniority and what they bid for).
Reserve is on-call at home, with the ability to show up at the airport within, say, 1 or 2 hours of being called.  This is for pilots who call in sick etc, a number of hours before departure.
Ready Reserve is you show up in uniform and with your gear at the operations dept of the airline and hang around in the crew lounge in case they need a crew right now. If they don't, you go home at the end of your shift without flying.
A pilot who is incapacitated just before a flight will be replaced with someone who is on Ready Reserve, and if none are available, then the flight takes a delay until a Reserve pilot can show up.

These may also be known as “long call” and “short call” reserve, in reference to how quickly pilots have to show up after receiving the call from Crew Scheduling.

Of course, airlines don't have reserve pilots available at each and every airport, only in major locations (usually their "bases", from which pilots depart), so if a pilot becomes incapacitated somewhere else (after having flown a segment from their base to another airport), then the flight is either delayed until a pilot can get to that airport or cancelled.

Do they get paid for these statuses? At what %?

Most airlines have a pay structure based on hours flown, with a minimum guarantee, which you could think of as a base salary.  Typically, 75 or 80 hours per month is your minimum base pay.  On a reserve duty period you would get paid no less than your guarantee minimum, so even if you don't fly at all you still get that.  Some pilots who can afford to live on the minimum and who don't want to fly all the time, may bid for as many reserve duty periods as possible so they can hang out at home as much as they can, but at a really busy airline, especially regionals, you still end up flying a lot.

This base pay is particularly relevant for pilots right now, as nearly all of them are on base pay right now - few are getting more hours than the base, but they haven't laid anyone off yet from the major carriers (though that'll undoubtedly change soon).  A pilot I know usually is out for 4 days a week home 3, making about 100 hours/month; now he is out on a couple day trip once every few weeks, for maybe 40 hours a month a most (and usually even less).

Yeah that's what I'm seeing too.  The regionals have laid a lot of pilots off however.

There may also be the option of extending the shift of a pilot who was planned for a short shift.

Yes overtime. This is limited by complex on/off duty time rules.

The co-pilot cannot fly the plane alone, as invariably the sort of aircraft you refer to are multi-crew - they must be flown by more than one pilot.
Airlines have an on-call list which is a bank of pilots who are not rostered to fly, but are on standby for the exact sort of situation you describe.

Comments are not for extended discussion; this conversation has been moved to chat.

Each month on your flying roster, you have a couple of days of standby. For those who do not know what standby is,it is basically a set of crew on standby( hence the name) to operate a particular flight just in case anyone call sick or unable to fly due to any unforseen circumstances.
more details see here


text:
Why do I get an overspeed warning at 250kts below 10,000ft in Microsoft Flight Simulator?
I'm flying the Cessna CJ4. I get overspeed warnings at 250kts when below 10,000ft, and the speed indicator has red lines at 300kts. Are these warnings triggered because it'll damage the plane to go that fast, or because it's illegal to go that fast that low? What's the distinction between 250kts and 300kts?

Related: Did this aircraft illegally exceed 250kts below 10,000ft?

While no experton the Cessna CJ4, it makes sense to me that the cause would be due to the fact that it is an FAA regulation not to exceed 250 KIAS below 10,000 feet MSL. After all, you have stated that the airspeed indicator has Vne at 300 knots.

Also, the documentation that I find from Textron says that the Vmo between 8,000 and 27,900 feet is 305 KIAS. Where as the maximum cruise speed at 14,000 pounds and 31,000 feet is 451 KTAS. Do the visual indicators (red lines) change with altitude? Hope that helps.

If you’re talking about MSFS 2020, I wouldn’t worry too much.  There are way too many flight model errors in that game.

@DeanF. Aviation is global. Please refrain from going straight to mentioning FAA regulations, this isn’t an American site, but a global one.

@ob318 - Thanks for the feedback. This is a global website. And, aviation is a global endeavor. These facts do not in any way make the regulations of any civil aviation authority of any country irrelevant. Another poster’s insights regarding EASA or CAA regulations will enlighten us all and are just as valid if they wish to post them. Take into consideration my response to the question was posted as a comment and not an answer. Feel free to voice your own interpretation of the reasons for the overspeed warning.

@ob318 - Bear in mind that the questions’s original poster has a profile stating that he is from Virginia. The Cessna Citation CJ4 (Model 525C) was manufactured in Kansas. Its first flight was in Kansas. Its original Type Certification was issued by the FAA. Microsoft (the manufacturer of the flight simulator software) is headquartered in Washington. And, the use of feet and knots in the question somewhat (but not entirely) narrows the geographic location. These all make my rough guess not completely out of the ballpark.

Most likely Cessna introduced a speed switch that is controlled by an aneroid.  Anytime you are below 10,000 FT MSL, the aneroid activates that switch.  If you go above 250 knots, the overspeed warning will sound.
As far as why that is the case, in the United States you are limited to a speed of 250 KIAS below 10,000 FT.  I would imagine this is also the case for most other countries.  The FAA realizes that most small airplanes with a much slower airspeed travel only below 10,000 FT MSL so the FAA is providing a safety margin to prevent in-flight collisions.
The structural limit of the airplane would not be a factor at 250 KIAS hence the red line at 300 KIAS.  I would imagine 300 KIAS deals more with structural stability than anything else.
My question... can a slow-tation go that fast?  :-)

Re travelling only below 10,000 FT MSL, maybe east of the Mississippi.  Further west, that's not always such a good idea.  Lots of mountains taller than that.  FTM, there are a couple of airports where 10K ft isn't even pattern altitude: https://www.boldmethod.com/blog/lists/2014/08/10-highest-airports-in-the-united-states/

Are you suggesting that the overspeed warning would come on at 250kt below 10,000ft in the real aircraft? I seriously doubt that. My guess is that this is a feature of the simulator. The warning system description says "Overspeed annunciations have no visual counterpart warnings. The voice or tone warnings are continous while the airspeed is above VMO/MMO on the copilot's airspeed indicator." There is nothing mentioned of 250kt below 10,000ft.

Agree with @Bianfable What if ATC instructed you to fly at 260 knots? You would just have to live with the warning? Cockpit warnings generally only relate to the limits of the aircraft, not regulatory limits (which can change at any time and are not always applicable)

Airplanes departing U.S. west coast airports on trans-Pacific flights often get permission to exceed 250 kts if  the fuel load requires the excess airspeed to achieve reasonable climb performance. I think the special airspeed approval is part of Clearance Delivery. Would be really annoying to have that warning go off.

As V(MO) is approached in a jet aircraft, the overspeed warning is activated to protect the structural integrity of the aircraft and ensure it remains inside of the acceptable structural envelope. Pilots need to react without hesitation to an overspeed warning - usually by reducing the throttles to flight idle and therefore bringing the speed outside of the warning envelope. As Dean F mentioned in his comment, the FAA prohibits flight over 250kt below 10,000 ft MSL as a measure for traffic control. That can only be exceeded when the controlling ATC agency issues a speed clearance, often in the form of a "high speed climb out approved" clearance. In addition, manufacturer guidance needs to be followed when approaching the high end of airspeed in jet aircraft as to how to recover from an overspeed or approaching V(MO)/V(NE) airspeed.
See https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/airplane_handbook/media/17_afh_ch15.pdf page 15-9 for more information.


text:
How can I estimate wind speed and direction in VFR?
I am new here, I started to do VFR navigation (no G1000) so I try to deal with the wind.
I notice that I have some problems to find the wind speed and direction during flight. I am going to try to explain better: I am looking for some easy method to find the values (for example no CRP5 or too long trigonometry formula), something that can give me a fast idea from where the wind is blowing and the speed so I can anticipate the correction.

Please tell us what navigational aids and tools you have.

If you are doing paper navigation with an E6B, then your preflight planning should have included wind correction angle calculations. When you are in the air, you could do that same process in reverse with your actual track as the input. But in practice, we just eyeball it: “I’m drifting a little further north than planned, so I’ll point the nose a little more south to compensate.”

Are you really looking at how to estimate the wind, or how to estimate your correction given you know approximately what the wind speed and direction is from your pre-planning? You mention CRP5/Trig but neither of these tools will help you estimate wind speed/direction!

@Raffles navigation I have the Garmin GNS 430( I know I can make the GPS calculate it), HSI and a CDI.

@StephenS I don't use the E6B but yes in my flight plan I have already make the correction for the heading but because the wind is variable I wanted to have a faster  way to estimate the wind.

@Jamiec how to estimate the wind in certain leg without using my preplanning, in reality at least with the CRP5 at school we were able from track/heading/GS/TAS to calculate the wind direction and speed, the fact is that is not really the fastest way to do.

I think you might be overthinking this a little. If you get from A-B a bit slower than expected, you had a slightly higher headwind than you planned. Adjust next leg as appropriate (estimating as you go). If you are arriving left of track, you had a slightly higher wind from the right than expected... adjust as appropriate. It's a perfectly inexact but workable science.

Does this answer your question? How does a pilot know if he has headwind, tailwind or crosswind?

Does this answer your question? How can the wind speed and direction be calculated from on-board measurements? I know you said you didn't want too much math, however you really only have two options: do the math, or just adjust continuously as you go. Assuming you're asking about simple VFR pilotage/dead reckoning in a light aircraft then there's no need to be very precise anyway. Most pilots will just adjust as needed.

I used to do this when I was flying in the bush on floats, where there is very little time for planning and you are in a flying environment where you are living by your wits (which is what made it such great fun).
The only thing that really works to any (limited) degree, just by observation in the moment, is to look for bodies of water and observe the telltale signs of the surface winds.  Wave or wavelet size, streamer markings, lee side shoreline wind shadows. Or better, smoke columns from fires.
The wind typically veers (rotates clockwise) with altitude, so if you see a lake or someone burning something that suggests the wind is blowing on it from the west, with signs that suggest it's blowing at, say, 10kts, you can expect it to be more northwesterly the higher you go, and faster.  So if you guess the wind is 10kts and 270 at the surface, you can expect it to be maybe 300-ish and 20-30 kts at, say, 4000 ft.
Those are just signs that can help you make a better wild guess.  In the absence of any ground signs, the only other thing you can do is hold a constant heading for a couple of minutes on a timed run between two points, and note the difference between heading and track, and difference between ground speed and TAS.  Ground speed same as TAS, wind is at 90 degrees to your course (or velocity is zero), less than TAS it's forward, more it's behind. Ground speed less than TAS and significant crab angle to the left, the wind is quartering left/front.  Lots of crab and minor GS penalty, closer to 90 deg off your left, less crab and more GS penalty, closer to straight ahead.
With a bit of practice you should be able to make an educated guess on direction within maybe +/- 30 degrees and velocity +/- 15 kts.  With everybody using moving maps these days, these are skills that are becoming long lost.

+1 for the second paragraph alone.  An old gliding instructor I knew used to point out the direction of waves and other telltales.

Assuming your GPS broke! You will need to know your track(course) and groundspeed, and heading and true airspeed. Heading is easy, it's on your HSI, and if you are maintaining a VOR radial to or from a VOR, you will know your track(course), and see the drift angle on the HSI. You will then know if the wind is coming from the left or right. If it's head-on or from behind there will be no drift angle and you will figure out if it is a headwind or tailwind after you calculate your groundspeed.
To know your TAS, you will either have to use your E6B or look it up from a table. Groundspeed can be obtained from your DME, take the distance flown for 1 minute and multiply it by 60, or 2 minutes and multiply by 30 if you want more accuracy. If you don't have DME, you could ask the ATC what it is if they have you on radar, otherwise you will have to do some accurate map-reading.
The difference between TAS and Groundspeed will tell you if you have a headwind or tailwind. You can then figure out approximately where the wind is coming from and how strong it is. If you need to know it accurately, make a scale diagram such as the one below or use your E6B.

A hand-held GPS can be very useful.  Holding airspeed constant, just take a few moments to turn to the heading where groundspeed is minimum (or maximum), and you'll know the wind direction and have a good idea of wind speed.  If you want more precision, you can then turn 180 degrees and note the groundspeed there.  This will get rid of errors due to density altitude, etc.  The wind speed is half the difference between the two values.  But to save yourself the time wasted in flying way off course, get the expected TAS off your E6B and compare that to the groundspeed you get flying either directly upwind or downwind, whichever involves less deviation from your intended course.
Continuing with the handheld GPS theme-- if you happen to be flying a glider in thermal updrafts, or doing a series of sustained constant-bank circles for any other reason, then when the track log screen is zoomed in to give a high resolution, the "curlicue" nature of the logged ground track will give you an immediate indication of wind direction and speed.  The overall direction of the track will show the downwind drift, and the less the "curlicues" look like round circles, the stronger the wind speed.
Of course, if you have any kind of GPS on board, you don't really need to know the wind speed and direction at all; you can just observe what heading takes you where you need to go, and note the groundspeed.  So I suppose your question was really intending to ask about methods not involving any kind of GPS!

Flying circles and observing how the intended center of the orbit moves can give the pilot an idea of the wind speed & direction.

True, but only when you are fairly low...

Very true... And there's another trick for those who fly even lower: Cattle usually put their backs to the wind...


text:
How can I work out Sea Level Pressure from QNH?
I am a little confused, is the QNH the current pressure at Sea Level? Therefore putting it into the altimeter will give your current altitude on the ground in pressure altitude relative to current sea level?
If not could someone please advise me on how to back calculate sea level pressure given the QNH and ground temperature.

Yes the QNH value is based on the atmospheric pressure taken at the measurement site, then adjusted to represent that same atmospheric condition at seal level based on the normal expected pressure change between sea level and the measurement site, and at the standard temperature lapse rate.  In other words, if the measurement site was 1000 ft above sea level physically, it's what the atmospheric pressure at the measurement site would be if you were to dig a 1000 ft deep pit at that spot and take the pressure measurement at the bottom of the pit which is physically at true sea level.
The adjustment is based on the lapse rate of the standard atmosphere, so an error is introduced in doing this adjustment if temperatures are significantly different from standard temperatures (59F at SL).  Normally not a big deal because everybody in the vicinity is using the same "erroneous altitude", so no harm no foul, but in cold weather this has to be taken into account for IFR operations because the error (altitude reading higher than it really is when temperatures are below standard) becomes significant for the safety of IFR approach operations, and correction tables have to be used, generally when doing approaches in below freezing weather, where the potential high reading error starts to become dangerous in terms of obstacle clearance and decision altitudes.

Thank you very much!

QNH Is the mean sea level pressure which is

Mean sea level (MSL) (often shortened to sea level) is an average level of the surface of one or more of Earth's bodies of water from which heights such as elevation may be measured
source: wikipedia

So yes, putting QNH into your altimeter gives you your altitude above mean sea level.

If my memory serves me right, this is only exactly true if the temperature lapse rate follows the 1.98°C per 1000ft from the ISA.


text:
What are the lines of triangles on the DCA RWY 19 River Visual approach chart?
A recent update of a certain flight simulator made me revisit this chart and I had not noticed the lines of triangles (at the Chain Bridge / Roosevelt Bridge etc, but not at the Key Bridge) in a past version, years ago.

What are they?  I couldn't find the information in the FAA Chart User's Guide.

So, applying some local knowledge, the Key Bridge is a high arch bridge in that it is a good distance above the water level, and the other ones listed, Rochambeau, Memorial , Roosevelt, and Chain Bridge are all "low" bridges, more like causeways.
I tried looking for a chart legend that said this, but I wasn't able to find one.

They represent the bridges. You can use the bridges to gauge where to be on your approach.

As the Q notes, the Key Bridge doesn’t have them. What’s different about the bridges that do?


text:
How can the lift induced drag for a wing be calculated?
I have found a lot of information to calculate drag coefficients and I know that total drag can be calculated by
$$ D = \frac{1}{2} \rho u^2 S C_d $$
However I was wondering, if I substitute the zero lift drag coefficient into this equation is it correct to assume the value produced for the drag force would be the parasitic drag whilst the remainder of the total drag is made up of lift induced drag?

Related: how is the induced drag calculated for a wing with elliptical planform

Just a reminder, the above formula is not total drag,  you might know this already, what you are calculating  is drag produced in response to the generation of lift with respect to an airfoil, remember there are many other forms of drag, for example profile drag, parasitic drag etc. Total drag will be the sum of all of them.

Induced drag is the portion of the lift force that opposes motion.  Induced drag exists even when the drag coefficient CD in your equation is zero.

Lift is perpendicular to the air flow relative to the wing.  Imagine a wing moving right to left across your screen.  The air is moving left to right relative to the wing.  If there's no vertical induced airflow then the lift is vertical and there's no induced drag.  However, lift deflects the air down, so typically the air relative to this wing is not moving exactly left to right, but is tilted down slightly.  Hence, the lift, which is perpendicular to that airflow, is actually tilted back (right) slightly.  That means a (typically small) portion of the lift is "pushing this wing back," opposing its right-to-left motion.
If you know trigonometry, induced drag is lift times the sine of the inflow angle, $ L\sin \phi $.  The inflow angle is the angle of the airflow relative to the horizontal in this picture.
There's a picture of exactly this at the bottom of this page in the induced power section.  (Induced power is the power required to overcome induced drag.)

If lift is the component perpendicular to the air flow, as you correctly state in the second paragraph, then it cannot oppose motion. Also the question is about wing, so you shouldn't mix in factors only relevant for propellers—in which case you should also be talking about induced power, not drag.

Lift can oppose motion.  This is exactly the case provided in the example.  Motion is right to left, but net airflow is NOT left to right because you must include induced airflow, which "tilts it down" as shown in the picture.  The reason it's called induced drag is because it's associated with this induced airflow.

No! Lift is defined as the component perpendicular to relative wind, and relative wind is defined as the free stream velocity, that is reciprocal of the aircraft motion in the air. The force due to circulation is tilted back, and this is the induced drag. But the definitions are such that this isn't what is called lift. Lift is one component of this force and induced drag is the other.

Please check wikipedia or any standard book or any aerodynamic software.  It's well defined - lift is perpendicular to the flow.  The flow includes more than motion, e.g. wind, induced velocity, sometimes interference from other objects.  Another way to think of this is that it wouldn't make sense otherwise - a wing cannot discriminate flow due to motion from other flow sources.

Wikipedia says: “Lift is the component of this force that is perpendicular to the oncoming flow direction.” (emphasis mine). So it does not include induced velocity and other things. And of course there is no wind in the reference frame of air mass.

The Wikipedia quote is correct.  The issue is that you're trying to exclude induced velocity from the oncoming flow.  It and other sources of flow must be included.  It wouldn't make sense otherwise.  Please read https://en.wikipedia.org/wiki/Lift-induced_drag or other references carefully.  If you don't understand that, maybe you could post a new thread and we could discuss there.

So lets go to the reference and flip a page from What is Lift (which is less clear than WP) to What is Drag which unambiguously states that “Drag acts in a direction that is opposite to the motion of the aircraft. Lift acts perpendicular to the motion.”. And then “The local angle of attack of the wing is increased by the induced flow of the tip vortex, giving an additional, downstream-facing, component to the aerodynamic force acting on the wing.”—note they don't call it “lift”.

I admit the NASA link for kids confuses this topic - they oversimplify definitions there.  If you want to use that as your source it maybe OK for very high level talk.  However, if you want to understand this this or apply it, you'd need to account for the total flow including all sources (induced flow being a significant one).  Again, the prior link I  provided will show you how it works.

No, they use exactly the same definition as everybody else. And remember, we are in complete agreement about the actual phenomenon. The only disagreement is whether you decompose aerodynamic force due to circulation to lift and induced drag, or decompose lift to induced drag and…. what?

I guess you are trolling.  I even read the NASA link you quoted above and it clearly states the motion you quoted was "motion between the object and the fluid."  They further clarify it "makes no difference whether the object moves through a static fluid, or the fluid moves past a static solid object."   E.g. if  you're flying 100kts (ground speed) and there's a 20kt wind, you have to include that wind.  If something's (fan?) is blowing a 10kt wind down on you, must include that too.  If the body is inducing a 10kt wind down, must include that too.

I am, all the time, talking about motion between the object and the fluid. Specifically, motion of the fluid far enough from the object not to be affected by it relative to the object. That's the definition of relative wind. That precisely matches what the NASA article says. That does not include any induced motion, which I understand according to the standard definition as motion of the fluid affected by the object.

Here are a couple more links.  To save yourself time you can scroll right to the diagrams showing the airfoils, the total flow and the LIFT vector.  What is the lift perpendicular to in all these diagrams?  And how do they define induced drag?  https://www.perfectedflight.com/the-truth-about-induced-drag/.  http://www.ase.uc.edu/class/AEEM456/Section_2_Notes.pdf

The second one indeed defines lift as perpendicular to the local flow. The first one is funny, because it first defines it perpendicular to relative wind, then renames it to “effective lift” and redefines lift as perpendicular to local flow. Ok, so there are clearly two inconsistent definitions.


text:
How does the heading selector on the ADF work?
How does the ADF indicator work in terms of pointing the needle in the direction of the NDB signal? I understand that the ADF needle points towards the direction of the NDB signal for a given frequency, but when a pilot tunes in the ADF signal, the heading ring does not change when the ADF was tuned into the frequency, only the direction of arrow changes.
So my question is, how do you use the heading selector when navigating with the ADF? And is it important to change the heading?

In the image, let's assume the aircraft is heading 030 degrees, but the heading on the ADF does not change to 030 degrees only the ADF needle changes its direction. Why is this?
If I were to turn from 030 degrees to 180 degrees, the needle would only change its direction not the heading of the ADF.

Your question doesn't make much sense at the moment. An omnidirectional bearing indicator (i.e. CDI) doesn't have anything to do with ADF. It's used for a completely different type of radio navigation (VOR, ILS/localizer, GPS). Why would you think the CDI would change due to use of this completely unrelated radio, the ADF? Possibly if you include some pictures showing what exactly you're asking about and explaining exactly what your expectations are, the question could the salvaged.

@PeterDuniho I bet he’s referring to the heading ring.

@StephenS yes I am referring to the heading ring. Do you have an answer?

If you mean "the heading ring", then that's what you should write. There's no reason that the term "omnidirectional bearing" should appear anywhere in this question, as far as I can tell. Your question continues to have confusing/misleading wording. Adding the images helps, but you still need to fix the wording.

It's just a manual compass card (or some call it a heading ring), not an "omnidirectional bearing".  The ADF needle just points to the station (NDB or AM radio station) relative to the airplane; that's it that's all.  If the needle's at 9 o'clock, the station is off your left wing.  The compass card is just a reference device to provide a mental shortcut for determining the magnetic compass bearing of the station relative to the airplane when you are flying a particular heading.
To use, you set the compass card to the heading you are currently flying, and this gives you a quick way to see the compass direction of the ADF station relative to the airplane.  Ideally, you would want the compass card slaved to a gyrocompass system so it shows your heading directly and fancier systems (RMIs) do that, but a standalone ADF doesn't have that feature so you have to set it yourself.
The NDB in the picture is 60 degrees off the nose of the plane. You're flying a heading of 030 and want to know the actual compass direction from the plane's current position to the NDB; in other words, the compass heading to fly to proceed direct to the NDB.
You could just subtract 60 from 30 to get 330 as the bearing to the station, but instead of having to do that little bit of mental math, you dial the compass card to 030 and there's the needle pointing at 330.  Of course, the card is just fixed where you set it, so you have to make sure your actual heading matches the card setting at the time you check the reading.


text:
Why do airline toilets delay for a few seconds before flushing?
I have noticed that when I push the toilet flush button in a regular passenger airliner, it takes several seconds (perhaps 2 or 3) before the toilet actually flushes.
What is the reason for this delay?

Probably charging the flux capacitors.

Most passenger aircraft of today (747, A380, widebodies of any kind) use vacuum-flush toilets.  It takes time for that system to go through. It also has to coordinate lids into the waste storage container that is usually fireproofed.
Those 2 seconds took decades to develop and keeps the odor and fires out!


text:
Is it normal for airport to transmit unmodulated carrier on its ATIS frequency for extended periods of time?
So I'm around 4 km away from the City-Airport Mannheim (EDFM/MHG). Various websites tell me that its ATIS frequency is 136.550 MHz.
When I tune to 136.550 with my VHF AM receiver, I can see a strong carrier, with no modulation at all. I've listened to it for several hours, on different weekdays and during different times of day.
So my question is: Is this usual behavior or not? I'm aware that the airport in question doesn't see much traffic, but I'd sort of expect the ATIS to be either running, when needed, or switched-off, when not needed.

@mins Yes, the receiver is in AM mode (only settings it has in this band are 25 kHz step or 8.33 kHz step) and I can hear both ATC and aircraft on other frequencies. Right now, I'm listening to 126.325 MHz and 123.275 MHz and I can hear both ATC and aircraft fine on them. Also, I couldn't find to whom are those frequencies assigned on many websites I've seen. Is there another frequency change in  progress?

@mins No, but on the other side, there's very little local traffic. I can mostly hear planes going to the Frankfurt (and they report their ATIS). I did hear activity on the MHG tower frequency a couple of times, but I haven't hear any of them report ATIS information yet. Basically, I don't have enough information to conclude if they're actually reporting ATIS or not.

You'll find frequencies and hours in this AIS documentation at section 2.18


text:
What do solo pilots do between reporting points on longer flights?
On some IFR flights, it can be a long time between waypoints. Obviously you must continue monitoring ATC for instructions, but during the rest of the "idle" time, what tasks do pilots have that keep them occupied?
I'm specifically interested in what solo pilots do.

Eat carrots. Listen to podcasts. Do paperwork.

The short answer is that you keep checking everything in the aircraft is doing what it should. For light piston GA operations, one common acronym for en route checks is FREDA. Here are some things that could be included (pilots often use their own checklists for things like this):

Fuel. How much have I burned? Is my navigation log up to date? Have I burned the amount I expected? How much longer can I fly for before I have to land? Which airports are within my current range ring? Is it time to switch tanks? Is the aircraft still within weight and balance limits? Is the airport where I planned to refuel still the right place to go?
Radios. Do I have all my radios set to correct and useful frequencies? How am I going to identify my next waypoint? Do I need to tune and identify a new VOR? Have things been suspiciously silent for a while? Should I file a PIREP? Do I need to tell ATC I need a deviation for weather? What's the latest weather information from ADS-B or another source? Can I guess which frequency ATC is going to hand me off to next? Did ATC ask me to report at a certain time or place?
Engine. Are all temperatures, pressures, gauges etc. showing the values I expect? Have I leaned the mixture properly? Are the exhaust gas temperatures correct? Is manifold pressure correct for this altitude? Has anything changed unexpectedly since the last time I checked them? If the engine dies right now, where am I going to land?
DI to compass. Reset the directional indicator to match the wet compass, to avoid gyroscopic precession errors.
Altitude. Is this altitude correct for my current heading? Is this the altitude I was assigned? If I lose comms now, what altitude should I fly at? Do I know what terrain is below me? What's ADS-B showing me right now? Any potential traffic conflicts? If I encounter icing here, will I descend, climb, or turn around? Is the autopilot correctly configured? Have I entered the current altimeter setting in all the instruments?

After you've worked through all that, it's usually time to go back to the beginning and start again :-)
Of course, there are plenty of other things that pilots are likely to be doing, like having drinks or snacks, taking pictures, admiring the view, listening to music, trying to find their spare headset batteries at the bottom of their flight bag, and so on.
But an IFR flight - or any flight - is never just sitting back between waypoints and waiting for ATC to call. The point of the constant checks is to detect any problems as soon as possible. For example, if you notice the oil pressure dropping gradually, you can take action while you still have engine power; if the first you know about it is that the engine suddenly stops then you have a big problem. Not only have you lost engine power, you're also not mentally 'primed' to deal with the situation and that could turn a tricky situation into a dangerous one.

Did I leave the iron on?

Also, for those of us who don't have autopilot systems, flying the airplane is a pretty important thing to do between waypoints. :)

Not long ago, I had my personal longest ever flight as a PPL: about 4 hours from Dallas, TX to Kansas City, MO, in a 172.  It was completely straight-line / DirectTo, and facing a steady headwind the whole way, so making a ground speed of less than 90kts.
I ran checklists about twice as often as normal, and re-did my fuel calculations very regularly (in part because of the extremely slow progress).
I listened to the ATC frequency, and tried to build a good mental picture of all the planes around me.
I went through every single setting and option on my MFD glass cockpit and iPad.
I watched the scenery, both for visual navigation (despite my GPS), and just to admire the view.
Even after all this, the flight was pretty boring near the end, and I'm glad I don't do flights that long very often.


text:
What does "With One Minute Weather" Mean?
Yesterday I was listening to LiveATC at McClellan Field (KMCC) since many CAL Fire Tankers are stationed there and there's a lot of activity recently.
As the tankers returned from their bombing runs, they called McClellan Tower and reported they had the "One Minute Weather".
Most seemed to be flying VFR if that matters, although the Tower was handing out Squawk codes to those that requested them (on departure, probably for better TCAS reporting, coordination and general awareness I presume).
I'm unfamiliar with the weather report "with one minute weather", what does it mean? Is it a quick way to report they have the latest ATIS information?

Squawk codes aren't just for IFR, almost every time I fly out of a controlled airport I'm given a squawk code. The only time you want to use 1200 (still a squawk code) is if you are in uncontrolled airspace, flying VFR, and don't want radar services.

It's used at uncontrolled airports to tell approach controllers that you've got the AWOS/ASOS there. I believe the tower at KMCC is temporary (probably for firefighting).
The AIM 4-3-26 is snappily titled Operations at Uncontrolled
Airports With Automated Surface Observing System (ASOS)/Automated Weather Sensor System(AWSS)/Automated Weather Observing System (AWOS), and says:

If ATC service is required for IFR/SVFR approach/departure or
  requested for VFR service, the pilot should advise the controller that
  he/she has received the one−minute weather and state his/her
  intentions.
EXAMPLE− “I have the (airport) one−minute weather, request
  an ILS Runway 14 approach.”

It's also in the Pilot/Controller Glossary:

ONE-MINUTE WEATHER− The most recent one minute updated weather
  broadcast received by a pilot from an uncontrolled airport
  ASOS/AWSS/AWOS.

And this from the ATC Orders 5-10-2:

Automated weather observing systems may be set to provide one minute
  updates. This one minute data may be useful to the pilot for possible
  weather trends. Controllers provide service based solely on official
  weather, i.e., hourly and special observations


text:
Why did the altimeter in an F-16 jump suddenly as it passed through Mach 1?
In this video, Destin — the creator of YouTube channel Smarter Every Day — rides in an F-16 with a USAF Thunderbirds pilot. If you start watching the video at the 11:06 mark, you will see what happens when the aircraft passes through Mach 1, namely, that the altimeter reading suddenly jumps.
Destin explains that this jump in the altimeter reading is because the air pressure downstream of the normal shock wave that is impinging on the pitot-static tube of the aircraft is lower than the air pressure upstream, but by the laws of compressible airflow, this would be total air pressure, not static air pressure.
As static air pressure, which is sensed by the altimeter, is always higher downstream of a normal shock wave, why is it that the altimeter reading registers a sudden jump and not drop instead?

The altimeter doesn't measure static air pressure, it measures actual air pressure. So, to get an accurate reading of the static air pressure, the static port has to be carefully placed so that the ram air pressure (caused by the forward motion of the plane ramming into the air) and the slipstream pressure (caused by air rushing past the static port opening) cancel each other out (or nearly so).
So, Destin is correct: The actual air pressure after the shockwave is lower, causing a jump in the displayed altitude.

Hi, HiddenWindshield. Isn’t the altimeter designed to sense only static air pressure in straight and level flight? Destin was absolutely correct in saying that the total air pressure behind the shock wave is lower, but his explanation doesn’t seem consistent with the fact that the F-16’s altimeter senses air pressure from the static taps of the F-16’s nose-mounted air data probe (please refer to Page 1-139 of the F-16C/D flight manual).
Also, does the jump in the altimeter reading indicate that it’s unreliable after passing through Mach 1?

@Transcendental The data probe acts like a tiny airplane, with its own ram air pressure from the front and slipstream pressure on the side, and stagnation point where the two cancel out. The tap for the altimeter would be on the side of the probe, as close as possible to the calculated stagnation point. (Actually the diagram seems to show two taps, one on each side, which would help keep the altimeter accurate if flying uncoordinated.) And I wouldn't call the altimeter "unreliable" past the speed of sound, just that it's going to be off by a fixed amount that varies with speed.


text:
Why is the aviation industry taking so long to move away from the tube with wings model?
The industry is spending billions on maximising fuel efficiency and reducing other costs associated with the tube-with-wings model. When will novel designs like semi-dirigible and lifting body arrive, what's the delay, surely the industry will be forced into a corner before the latest batch of airliners are due for retirement?

So what's wrong with tube-with-wings?

Welcome to aviation.SE! It isn't clear from your question why you think that current designs need to be replaced, or how manufacturers will be "forced" to rethink their approach. If you can give more specific background then you may get a better answer.

Also related: Why are there no blended-wing passenger airplanes in operation?

Lifting body designs are better than... well, anything that is currently in service? Maybe we can put them into service right after the all-electric supersonic jet Musk was going on about.

In aviation there are simply configurations that work the best when working out all the compromises caused by competing and contradicting objectives, and these become timeless and continue for many decades until some completely new physics paradigm comes along to upset the apple cart.
So, the tube with wings is the most efficient way to do it, not from some optimized theoretical single minded objective standpoint, but from the real world need to balance this goal against that goal.  You need to minimize frontal area, and to get the most people in the smallest frontal area, you have to arrange them lengthwise.  But not too long, so at some point you have to make the tube wider instead of longer.  A tube, low in drag, efficient structurally and easy to make, can't be beat.
The various radical approaches almost always fall short in key ways, which is the real reason you don't see them.  That doesn't mean stopping experimentation, because some day someone will come up with a radical configuration that sets a new standard while managing to meet all sorts of secondary needs, and then everybody will start to copy that configuration.
I always like to point out the ultimate engineering sweet spot as the pinnacle of this sort of thing, and really, probably the originator of the "tube with wings" concept - the Douglas DC-3, the greatest engineered conveyance of modern times.  This is a set of engineering compromises in such perfect balance, that eighty five years after it was designed, at the end of the second decade of the 21st century, they are still purchased and operated as working machines to earn a living for somebody, pretty much as they were originally built, as opposed to being operated for show or fun or as a museum piece.  That's engineering perfection, the grandfather of all modern airliners, still making money for people, the original tube with wings.

I share your enthusiasm for the DC-3 design. However, the fuselage was not a pure tube at the time, until the super constellation the fuselage was aerodynamically shaped.

Well it wasn't square or triangular.  Close enough.  The Connie had no straight lines at all so you wouldn't really call it tubular either.

I'm the only one who read the last paragraph with an epic cinematic music playing in my head?

Rofl.  That's the idea.  It really is quite amazing isn't it.


text:
How much simulator time can I use towards a part 61 instrument rating?
I am doing Instrument Rating under part 61 with a CFII.

To meet the 50 hours cross country requirement (d 1), can I log some of the PIC time in a simulator?
There is a 20 hours limitation on the use of simulator (h 2). So, if I have 40 hours of simulator time and 15 of them are cross country, can I use those 15 hours towards the cross county requirement and the other 5 hours towards the 40 hours requirement (d 2)?

(d) Aeronautical experience for the instrument-airplane rating. A
  person who applies for an instrument-airplane rating must have logged:
(1) Except as provided in paragraph (g) of this section, 50 hours of
  cross-country flight time as pilot in command, of which 10 hours must
  have been in an airplane; and
(2) Forty hours of actual or simulated instrument time in the areas of
  operation listed in paragraph (c) of this section, of which 15 hours
  must have been received from an authorized instructor who holds an
  instrument-airplane rating, and the instrument time includes:
(i) Three hours of instrument flight training from an authorized
  instructor in an airplane that is appropriate to the
  instrument-airplane rating within 2 calendar months before the date of
  the practical test; and
(ii) Instrument flight training on cross country flight procedures,
  including one cross country flight in an airplane with an authorized
  instructor, that is performed under instrument flight rules, when a
  flight plan has been filed with an air traffic control facility, and
  that involves—
(A) A flight of 250 nautical miles along airways or by directed
  routing from an air traffic control facility;
(B) An instrument approach at each airport; and
(C) Three different kinds of approaches with the use of navigation
  systems.
(h) Use of full flight simulators or flight training devices. If the
  instrument time was provided by an authorized instructor in a full
  flight simulator or flight training device—
(1) A maximum of 30 hours may be performed in that full flight
  simulator or flight training device if the instrument time was
  completed in accordance with part 142 of this chapter; or
(2) A maximum of 20 hours may be performed in that full flight
  simulator or flight training device if the instrument time was not
  completed in accordance with part 142 of this chapter.

The simulator doesn’t meet the definition of aircraft.

§61.1   Applicability and definitions.
Cross-country time means—
(i) Except as provided in paragraphs (ii) through (vi) of this
definition, time acquired during flight—
(A) Conducted by a person who holds a pilot certificate;
(B) Conducted in an aircraft;
(C) That includes a landing at a point other than the point of
departure; and
(D) That involves the use of dead reckoning, pilotage, electronic
navigation aids, radio aids, or other navigation systems to navigate
to the landing point.
(ii) For the purpose of meeting the aeronautical experience
requirements (except for a rotorcraft category rating), for a private
pilot certificate (except for a powered parachute category rating), a
commercial pilot certificate, or an instrument rating, or for the
purpose of exercising recreational pilot privileges (except in a
rotorcraft) under §61.101 (c), time acquired during a flight—
(A) Conducted in an appropriate aircraft;
(B) That includes a point of landing that was at least a straight-line
distance of more than 50 nautical miles from the original point of
departure; and
(C) That involves the use of dead reckoning, pilotage, electronic
navigation aids, radio aids, or other navigation systems to navigate
to the landing point.

Thanks. I got confused by the "of which 10 hours must have been in an airplane". If cross county = conducted in an aircraft, I am not sure why would they word it like that.

@user41786 There are aircraft other than airplanes. Consider someone with a lot of helicopter time, for instance, who is transitioning to airplanes.